If init dies, log a signal which killed it, if any.

I just received another user's pleas for help when their init mysteriously died. I again explained that they need to check whether it died because of bad instruction, a segv, or something else. Which was an annoying detour into writing a trivial C program to spawn his init and print its exit code:

http://lists.busybox.net/pipermail/busybox/2012-January/077172.html

I hear you saying "just test it under /bin/sh". Well, the crashing init _was_ /bin/sh.

Which prompted me to make kernel do this first step automatically. We can print exit code, which makes it possible to see that death was from e.g. SIGILL without writing test programs.

The code is fairly self-explanatory. Compile-tested.

Changes in v.2: don't try to decode signal names, just print exit status in hex.

Signed-off-by Denys Vlasenko <[email protected]>

---
 kernel/exit.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

kernel/exit.c +5 -3

index 294b170..0c540a5 100644
@@ -710,8 +710,11 @@ static struct task_struct *find_new_reaper(struct task_struct *father)
 
 	if (unlikely(pid_ns->child_reaper == father)) {
 		write_unlock_irq(&tasklist_lock);
-		if (unlikely(pid_ns == &init_pid_ns))
-			panic("Attempted to kill init!");
+		if (unlikely(pid_ns == &init_pid_ns)) {
+			panic("Attempted to kill init! exitcode=%08x\n",
+				father->signal->group_exit_code ?:
+					father->exit_code);
+		}
 
 		zap_pid_ns_processes(pid_ns);
 		write_lock_irq(&tasklist_lock);
--

1.7.7.5

I just received another user's pleas for help when their init mysteriously died. I again explained that they need to check whether it died because of bad instruction, a segv, or something else. Which was an annoying detour into writing a trivial C program to spawn his init and print its exit code:

http://lists.busybox.net/pipermail/busybox/2012-January/077172.html

I hear you saying "just test it under /bin/sh". Well, the crashing init _was_ /bin/sh.

Which prompted me to make kernel do this first step automatically. We can print exit code, which makes it possible to see that death was from e.g. SIGILL without writing test programs.

The code is fairly self-explanatory. Compile-tested.

Changes in v.2: don't try to decode signal names, just print exit status in hex.

...

It's a bit user-hostile to print a hex number in such a context without the leading 0x. The %08 does provide a hint - users are unlikely to interpret 00000011 as 11. But still, I think...

kernel/exit.c renamed from kernel/exit.c~kernel-exitc-if-init-dies-log-a-signal-which-killed-it-if-any-fix +1 -1

@@ -711,7 +711,7 @@ static struct task_struct *find_new_reap
 	if (unlikely(pid_ns->child_reaper == father)) {
 		write_unlock_irq(&tasklist_lock);
 		if (unlikely(pid_ns == &init_pid_ns)) {
-			panic("Attempted to kill init! exitcode=%08x\n",
+			panic("Attempted to kill init! exitcode=0x%08x\n",
 				father->signal->group_exit_code ?:
 					father->exit_code);
 		}

_

Or maybe we should use %d. Does anyone use hex for exit codes?